#include <iostream>

using namespace std;

const int N = 1010;

long long qmi(long long a, long long b, int p) {
    long long res = 1 % p;
    while (b) {
        if (b & 1) res = (long long)res * a % p;
        a = a * a % p;
        b >>= 1;
    }
    return res;
}

// 组合计数模板
int C[N][N];
int get_c(int n, int k) {
    for (int i = 0; i <= n; ++i) {
        for (int j = 0; j <= i && j <= k; ++j) {
            if (!j) C[i][j] = 1;
            else C[i][j] = C[i - 1][j - 1] + C[i - 1][j];
        }
    }
    return C[n][k];
}

int main() {

    cout << get_c(3, 2) << endl;

    return 0;
}